[epper]

Wuala: http://www.wuala.com

Data is encrypted with your password on the client side, your password never leaves your PC. They published a paper on their security implemenation: http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4032...

It allows to synchronize multiple folders and it gives access to a certain number of previous versions. You can also share folders with friends, publicly or via a secret link.

It's cross-platform: Win, Mac, Linux.

I'm a happy customer since more than a year (it's free up to 2GB though) and I wonder why so few people know about it.

[mvrekic]

Problem with this approach is sharing and key management.

If you want to send something to someone, that means you need to securely communicate the key to them first or take the SpiderOak approach of "We guarantee security locally but if you share a file = file is shared unencrypted".

[epper]

True, but if you both are friends on Wuala you can do it easily.

Provided that no man in the middle attacks take place during the "friendship" operation :)